Lung cancer is a major lung disease and accounts for more than one-fourth of all cancer deaths. Therefore, research into causes of the disease, identification of genetic and environmental risk factors, and discovery of better diagnosis and treatment strategies are urgently needed. One strategy to combat lung cancer is to identify genes that normally suppress tumor development. We have developed the first genetically engineered mouse model in which claudin-7 gene is deleted. Knockout of claudin-7 using gene targeting approach resulted in hyperproliferation of lung epithelial cells. Heterozygous claudin-7 mice showed an increased incidence of developing spontaneous lung tumors. Importantly, claudin-7 expression is either disrupted or downregulated at the cell-cell junction in lung cancer cells, and the overexpression of claudin-7 reduced human lung cancer cell growth in culture. These studies prompted the hypothesis that claudin-7 plays important roles in lung cancer progression as a tumor suppressor. To investigate how claudin-7 suppresses cancer growth in cell culture as well as in mouse models in vivo, this project will address two specific aims. Specific Aim 1: To investigate the roles of claudin-7 in lung cancer cell growth and survival in culture. We will use flow cytometry, TUNEL imaging, Matrigel invasion assay and cell- cell dissociation methods to determine if the properties of cell cycle, apoptosis, as well as cell adhesion and invasion, are altered when claudin-7 is stably expressed in a claudin-7-deficient human lung cancer cell line NCI-H1299. These experiments will determine how claudin-7 reduces lung cancer cell growth. Specific Aim 2: To investigate environmental carcinogens on the growth of lung carcinoma in vivo and on tumor-host interactions in Cln7 mice. We will investigate if environmental carcinogens, such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), can induce a greater tumor incidence in Cln7 mice compared to Cln7 mice. We will also investigate whether reduced claudin-7 expression results in altered host cell-cell junction and adhesion, allowing inoculated Lewis lung carcinoma LLC1 cells to interact with the pulmonary microenvironment more favorably and metastasize more easily. This project will allow us to collect preliminary data to determine whether Cln7 mouse strain is a viable model system for studies of claudin-7 function in lung carcinogenesis. These studies will also lay the foundation for a future NIH RO1 project to investigate the molecular mechanisms of how claudin-7 functions as a tumor suppressor. PUBLIC HEALTH RELEVANCE: One strategy to combat lung cancer is to identify genes that normally suppress tumor development. Claudin-7 is important in limiting lung epithelia from uncontrolled cell growth, as revealed by our genetically engineered claudin- 7 knockout mouse model. It is now important to investigate whether mice deficient in claudin-7 are more susceptible for lung cancer formation when exposed to environmental carcinogens and how claudin-7 suppresses cancer growth.